1. Field of the Invention
The present invention relates to isocyanate-terminated quasi-prepolymers and to polyurethane/polyisocyanurate foams prepared therefrom. The quasi-prepolymers of the subject invention are prepared by reacting a stoichiometric excess of one or more organic isocyanates with a polyester polyol derived from phthalic anhydride or from the transesterification of polyethylene terephthalate scrap. The foams prepared from these quasi-prepolymers have low thermal conductivity.
2. Description of the Related Art
Rigid foams derived from polyisocyanate addition polymerization continue to be an important and expanding segment of the polyurethane industry. These rigid foams may be prepared by numerous methods resulting in foams having a wide variety of physical and chemical properties. One of the most important areas of application for rigid foam produced by polyisocyanate addition polymerization is in the area of foamed-in-place insulation. Such insulation is commonly found in refrigerator and freezer cabinets, chest-type coolers, refrigerated tractor-pulled trailers, and building panels and insulated doors. Another important area of application for rigid foams is laminate board for construction applications. Increasing amounts are being utilized in buses, trains, and, particularly, in aircraft construction where the high insulating capacity is combined with the suitable physical properties to produce a variety of structural components.
Because of the types of applications which rigid foams lend themselves to, the thermal conductivity of these foams is of critical importance. The insulating properties, or thermal conductivity, of rigid foams are expressed by the K-factor and aged K-factor. The K-factor is a measurement of the insulating properties (thermoconductivity) and aged K-factor indicates insulating properties over time. The foams prepared from the quasi-prepolymers of the present invention exhibit low initial thermal conductivity values and maintain low thermal conductivity values after prolonged periods of use. Lower thermal conductivity values, of course, mean better insulating ability.
One class of aromatic polyols which is commercially available comprises esters produced by esterifying phthalic acid or phthalic acid anhydride with an aliphatic polyhydric alcohol, for example, a diethylene glycol phthalate.
Another class of aromatic polyester polyols which is commercially available comprises esters produced by reacting polyethylene terephthalate (PET) with alkylene polyols. More particularly, scrap or waste PET can be digested (glycolized) with a diol or triol as disclosed in U.S. Pat. No. 4,048,104; treated with caustic monohydric alcohol, U.S. Pat. No. 3,728,287; treated with monohydric alcohol and ester exchange catalyst, U.S. Pat. No. 3,488,298; heated with glycols and vinyl acetate, U.S. Pat. No. 3,857,799; heated with bis ester solvents, U.S. Pat. No. 3,884,850; or dissolved in ethylene glycol and/or terephthalic acid and/or dimethyl terephthalate, U.S. Pat. Nos. 3,907,868; 3,701,741; 3,703,488; 3,776,945; and 3,257,335. The products of these digestion processes may be reintroduced into the process from which they originate.
Generally, it is known that polyurethane foam can be prepared by using PET scrap derived polyol as a minor percentage of the polyol component. Such foams are said to exhibit improved fire retardant properties, U.S. Pat. No. 4,223,068.
It is also generally known that PET scrap derived polyols can be used as polyol extenders in preparing polyurethane foams as disclosed in U.S. Pat. No. 4,506,090.
U.S. Pat. No. 4,636,530, entitled "Isocyanate Terminated Quasi-Prepolymers Useful for Preparing Urethane-Group-Containing Polyisocyanate Foams Having Low Friability" discloses rigid polyisocyanurate foams prepared from quasi-prepolymers prepared by reacting a stoichiometric excess of one or more organic isocyanates with a polyester polyol derived from the transesterification of dimethyl terephthalate process residue.
In U.S. Pat. No. 4,608,432, it is generally disclosed that polyester polyols prepared from the reaction product of polyethylene terephthalate scrap; at least one low molecular weight aliphatic diol; and at least one compatibilizer compound, are useful in preparing polyurethane and polyurethane/polyisocyanurate foams.